This invention relates generally to the generation of plasma within enclosed or confined volumes.
The generation of a steady state bulk plasma has recently received renewed interest for various purposes including basic plasma physic studies as well as use in commercial processes calling for generation of relatively large quantities of the plasma with uniformity and predictable properties.
The generation of plasma by ionization of low pressure gas within a cylindrical chamber, to which the plasma is radially confined by the magnetic field of a surrounding magnetic coil, is already well known in the art, as disclosed for example in U.S. Pat. Nos. 4,742,232, 4,745,338, 4,767,931, 4,810,935 and 4,857,809 to Biddle et al., Hollis, Jr., et al., Sato et al., Boswell and Torii et al., respectively. According to the Torii et al. patent, radial confinement of the magnetic field establishes narrow high density portion of the plasma along the axis of the cylindrical chamber. Axial confinement of plasma is effected by repelling grids at the axial ends of the chamber according to the Biddle et al. patent. The Biddle et al. patent as well as the Sato et al. patent disclose an electron emitting filament adjacent to one axial end of the chamber to ionize the gas therein for generation of the plasma.
The foregoing prior art patents fail to disclose or suggest effective techniques for obtaining uniformity in the plasma density along the axis of the gas ionization chamber to facilitate the determination of such plasma density with changes in plasma generating parameters such as magnetic field intensity and filament discharge current.
It is therefore an important object of the present invention to provide for the generation of relatively large quantities of plasma with uniform and predictable densities in its steady state.